1. Field of the Disclosure
The present disclosure relates to a display device, and more particularly, to a timing controller, a driving method thereof, and a display device using the same, which can solve an image-sticking problem.
2. Discussion of the Related Art
Flat panel display (FPD) devices are used in a various electronic devices, such as portable phones, tablet personal computers (PCs), notebook computers, etc. The FPD devices include liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light-emitting display devices, etc. Recently, electrophoretic display (EPD) devices are widely used as the FPD devices.
Among such display devices, organic light-emitting display devices use a plurality of self-emitting elements that self-emit light, and thus have a fast response time, a high emission efficiency, a high brightness, and a wide viewing angle.
FIG. 1 is a circuit diagram illustrating a structure of one pixel of a general organic light-emitting display device, and illustrates a pixel structure that are configured with two N-type transistors. FIG. 2 is exemplary diagrams respectively showing images displayed by a panel of the general organic light-emitting display device, and illustrates a state in which a logo 1 is displayed at a specific portion of an image.
As illustrated in FIG. 1, a pixel 50 of the general organic light-emitting display device are configured with an organic light-emitting diode OLED and at least two or more transistors T1 and T2 that are connected a data line DL and a gate line GL to control the organic light-emitting diode OLED.
An anode of the organic light-emitting diode OLED is connected to a first power source VDD, and a cathode of the organic light-emitting diode OLED is connected to a second power source VSS. The organic light-emitting diode OLED generates light having a certain brightness in correspondence with a current supplied from a second transistor T2.
Various circuit elements included in the pixel 50 control an amount of current supplied to the organic light-emitting diode OLED in correspondence with an image signal supplied to the data line DL when a scan signal is supplied to the gate line GL. To this end, the pixel 50 includes: the second transistor T2 (a driving transistor) that is connected between the first power source VDD and the organic light-emitting diode OLED; a first transistor T1 (a switching transistor) that is connected between the second transistor T2, the data line DL, and the gate line GL; and a storage capacitor Cst that is connected between a gate of the second transistor T2 and the organic light-emitting diode OLED.
Since the above-described organic light-emitting display device uses the organic light-emitting diode OLED that is a self-emitting element, deterioration can be made by various causes. When a deterioration difference between pixels occurs, a brightness difference and a color-sense difference are discerned, and a permanent image sticking remains.
That is, when the same data having a high brightness is continued due to a self-emitting characteristic of the organic light-emitting diode OLED, deterioration is caused by an object having a certain shape, causing a regularly-shaped image sticking in which the shape is recognized as an image sticking.
The regularly-shaped image sticking is progressively intensified in proportion to a degree of deterioration of the organic light-emitting diode OLED, and at the limit in which a reduction in brightness is recognized by a user, a service life of the organic light-emitting diode OLED is acknowledged as coming to an end.
The regularly-shaped image sticking is caused by a logo or the like. The logo bring the regularly-shaped image sticking recognition limit forward, and thus shortens a service life of the organic light-emitting display device.
For example, as shown in a portion (a) of FIG. 2, when a logo or various subtitles 1 (hereinafter referred to as a logo) is continuously displayed in a certain region for a long time, a plurality of the organic light-emitting diodes OLED corresponding to the region in which the logo 1 is displayed can be deteriorated. In this case, even though the logo 1 is vanished, an image sticking of the logo 1 can remain in the region.
In order to prevent an image sticking caused by the logo 1, a related art method compares pixel data for each frame to find a position of a logo, and lowers a brightness of image data corresponding to the position of the logo.
That is, the related art method compares all pixel data of a current frame and pixel data of a previous frame to determine a region, which has the same pixel data in a certain number or more of frames, as a logo region, and lowers a brightness of image data outputted to the logo region, thus preventing the logo region from being deteriorated.
To provide an additional description, the related art method compares pixel data (10 bit×4 sub-pixels, input video data) of a current frame and pixel data of a previous frame at a corresponding position (the same position). When the same or similar value is repeated in a certain number or more of frames, the related art method determines a corresponding region as a logo region, and when the pixel data of the current frame differ from those of the previous frame, the related art method determines a corresponding region as a non-logo region. The related art method applies a brightness reduction gain to a portion determined as the logo region irrespective of a peripheral portion, thereby lowering a brightness of the portion.
The related art method has the following problems.
First, the related art method does not consider a fact that a logo is classified into a background and an edge. That is, the related art method does not perform a special processing on an edge. For this reason, when a brightness of a logo region is lowered, an image quality of an edge portion is degraded.
For example, a portion (b) of FIG. 2 shows the logo displayed in the portion (a) of FIG. 2, and the letters ‘OCN’ is displayed at a portion of the logo region which is determined as having the logo. However, the logo region includes a portion except the letter itself (a background), namely, an internal space of the letter ‘O’, a space opened from the center to a right side of the letter ‘C’, and a space opened from a lower end to an upper end of the letter ‘N’.
However, as shown in a portion (c) of FIG. 2, the related art method uniformly lowers an entire brightness of the logo region which is determined as having the logo, and consequently lowers a brightness of a portion corresponding to an actual logo, namely, a brightness of regions near the actual logo portion, in addition to a brightness of a region corresponding to the letters ‘OCN’ themselves. For this reason, an entire image quality of the logo region is degraded.
Second, the related art method reduces a brightness of the logo region without considering a brightness value near the logo region. Therefore, when a brightness near the logo region becomes higher and thus a portion near the logo region becomes brighter, the logo region is shown as being relatively dark, causing a degradation in image quality.